There has been used in a manufacturing field of semiconductor devices a conventional plasma processing apparatus for performing a plasma process such as an etching process, a film forming process or the like by applying a plasma generated in a vacuum chamber on a substrate to be processed, e.g., a semiconductor wafer, a glass substrate for use in an LCD or the like.
As the conventional plasma processing apparatus, a so-called parallel plate plasma processing apparatus has been known. The parallel plate plasma processing apparatus has a vacuum chamber in which a plasma is generated by applying a high frequency power to parallel plate electrodes, e.g., an upper electrode and a lower electrode facing each other in parallel, and then applied on a semiconductor wafer loaded on one of the electrodes, e.g., the lower electrode.
FIG. 5 shows a schematic cross sectional view of the parallel plate plasma processing apparatus. A reference numeral 1 in FIG. 5 indicates a vacuum chamber. Installed inside the vacuum chamber 1 are a lower electrode 2 serving as a mounting table for mounting thereon a semiconductor wafer W and an upper electrode 3 installed thereabove so as to face the lower electrode 2 in parallel.
A plurality of pores 3a are provided at the upper electrode 3, so that a process gas can be supplied from the pores 3a toward the semiconductor wafer W in a shower-like manner. Further, an exhaust port (not shown) is installed at a bottom portion of the vacuum chamber 1. By pumping the process gas out of the vacuum chamber 1 via the exhaust port, an inner space thereof can be set under a desired vacuum state. Furthermore, a high frequency power of a predetermined frequency is supplied from a high frequency power source (not shown) to a space between the lower electrode 2 and the upper electrode 3, thereby generating a plasma of the process gas in the vacuum chamber 1. The plasma thus generated then acts on the semiconductor wafer W, so that an etching process of the semiconductor wafer W or the like can be performed. Besides, a gate 4 for loading and unloading the semiconductor wafer W into and from the vacuum chamber 1 is installed at a sidewall of the vacuum chamber 1. A focus ring 5 is installed on a mounting surface of the lower electrode 2 so as to surround the semiconductor wafer W loaded thereon.
In such a parallel plate plasma processing apparatus, a plasma processing state is affected by the distance (gap) between the parallel plate electrodes, i.e., the distance from the lower electrode 2 to the upper electrode 3 in case of the plasma processing apparatus illustrated in FIG. 5. Therefore, there is known an apparatus capable of vertically moving one of the electrodes (the lower electrode 2 in the plasma processing apparatus of FIG. 5) and varying the distance between the electrodes (see, e.g., Japanese Patent Laid-open Publication No. 2000-286242 (page 3-5 and FIG. 1)).
Further, since the lower electrode 2 is vertically movable in the plasma processing apparatus of FIG. 5 as described above, an expansible/contractible bellows 6 is installed between a lower portion of the lower electrode 2 and a bottom part of the vacuum chamber 1 to air-tightly seal off an opening portion of the bottom part of the vacuum chamber 1.
However, since the inside of the vacuum chamber 1 is maintained at a certain vacuum level while the outside of the vacuum chamber 1 is under atmospheric pressure, a pressure difference between the inside and the outside of the vacuum chamber 1 is generated. Thus, an upward force is continuously exerted on the lower electrode 2 by the pressure difference.
Accordingly, in case the gap between the electrodes is widened by, e.g., lowering the lower electrode 2, the lower electrode 2 should be lowered against the pressure difference, thereby requiring an enormous force. Further, even in a normal state, a large force is also required to prevent the lower electrode 2 from being pushed upward to thereby maintain same in position. In order to meet such a load, a power source, such as a motor or the like, for driving the lower electrode 2 requires a great driving force and a mechanical operating system requires a great ruggedness. However, in that case, a manufacturing cost of the apparatus or a footprint is increased.
Recently, there has been a trend towards a larger diameter substrate to be processed such as a semiconductor wafer or the like, e.g., up to 12 inch. Therefore, a diameter of the lower electrode 2 also needs to be larger in order to meet the scaling up of the substrate to be processed. Accordingly, a force exerted on the lower electrode 2 increases in proportion to its area up to, e.g., about 5000 N to about 10000 N. As a result, the aforementioned problems become even more serious and, thus, it is difficult to resolve such problems.
As described above, in the conventional parallel plate plasma processing apparatus, a great load is exerted on a device for varying the distance between the electrodes because of the pressure difference between the inside and the outside of the vacuum chamber, thereby increasing the manufacturing cost and the footprint of the apparatus. Especially, it is difficult to meet the scaling up of the substrate to be processed.